8.42. ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER

8.42.1. Name

VIDIOC_G_TUNER - VIDIOC_S_TUNER - Get or set tuner attributes

8.42.2. Synopsis

int ioctl(int fd, VIDIOC_G_TUNER, struct v4l2_tuner *argp)

int ioctl(int fd, VIDIOC_S_TUNER, const struct v4l2_tuner *argp)

8.42.3. Arguments

fd

File descriptor returned by open().

argp

8.42.4. Description

To query the attributes of a tuner applications initialize the index field and zero out the reserved array of a struct v4l2_tuner and call the VIDIOC_G_TUNER ioctl with a pointer to this structure. Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds. To enumerate all tuners applications shall begin at index zero, incrementing by one until the driver returns EINVAL.

Tuners have two writable properties, the audio mode and the radio frequency. To change the audio mode, applications initialize the index, audmode and reserved fields and call the VIDIOC_S_TUNER ioctl. This will not change the current tuner, which is determined by the current video input. Drivers may choose a different audio mode if the requested mode is invalid or unsupported. Since this is a write-only ioctl, it does not return the actually selected audio mode.

SDR specific tuner types are V4L2_TUNER_SDR and V4L2_TUNER_RF. For SDR devices audmode field must be initialized to zero. The term ‘tuner’ means SDR receiver in this context.

To change the radio frequency the VIDIOC_S_FREQUENCY ioctl is available.

v4l2_tuner

struct v4l2_tuner

__u32	index	Identifies the tuner, set by the application.
__u8	name[32]	Name of the tuner, a NUL-terminated ASCII string. This information is intended for the user.
__u32	type	Type of the tuner, see v4l2_tuner_type.
__u32	capability	Tuner capability flags, see Tuner and Modulator Capability Flags. Audio flags indicate the ability to decode audio subprograms. They will not change, for example with the current video standard. When the structure refers to a radio tuner the V4L2_TUNER_CAP_LANG1, V4L2_TUNER_CAP_LANG2 and V4L2_TUNER_CAP_NORM flags can’t be used. If multiple frequency bands are supported, then capability is the union of all capability fields of each struct v4l2_frequency_band.
__u32	rangelow	The lowest tunable frequency in units of 62.5 kHz, or if the capability flag V4L2_TUNER_CAP_LOW is set, in units of 62.5 Hz, or if the capability flag V4L2_TUNER_CAP_1HZ is set, in units of 1 Hz. If multiple frequency bands are supported, then rangelow is the lowest frequency of all the frequency bands.
__u32	rangehigh	The highest tunable frequency in units of 62.5 kHz, or if the capability flag V4L2_TUNER_CAP_LOW is set, in units of 62.5 Hz, or if the capability flag V4L2_TUNER_CAP_1HZ is set, in units of 1 Hz. If multiple frequency bands are supported, then rangehigh is the highest frequency of all the frequency bands.
__u32	rxsubchans	Some tuners or audio decoders can determine the received audio subprograms by analyzing audio carriers, pilot tones or other indicators. To pass this information drivers set flags defined in Tuner Audio Reception Flags in this field. For example:
		V4L2_TUNER_SUB_MONO	receiving mono audio
		STEREO | SAP	receiving stereo audio and a secondary audio program
		MONO | STEREO	receiving mono or stereo audio, the hardware cannot distinguish
		LANG1 | LANG2	receiving bilingual audio
		MONO | STEREO | LANG1 | LANG2	receiving mono, stereo or bilingual audio
		When the V4L2_TUNER_CAP_STEREO, _LANG1, _LANG2 or _SAP flag is cleared in the capability field, the corresponding V4L2_TUNER_SUB_ flag must not be set here. This field is valid only if this is the tuner of the current video input, or when the structure refers to a radio tuner.
__u32	audmode	The selected audio mode, see Tuner Audio Modes for valid values. The audio mode does not affect audio subprogram detection, and like a User Controls it does not automatically change unless the requested mode is invalid or unsupported. See Tuner Audio Matrix for possible results when the selected and received audio programs do not match. Currently this is the only field of struct struct v4l2_tuner applications can change.
__u32	signal	The signal strength if known. Ranging from 0 to 65535. Higher values indicate a better signal.
__s32	afc	Automatic frequency control. When the afc value is negative, the frequency is too low, when positive too high.
__u32	reserved[4]	Reserved for future extensions. Drivers and applications must set the array to zero.

v4l2_tuner_type

enum v4l2_tuner_type

V4L2_TUNER_RADIO	1	Tuner supports radio
V4L2_TUNER_ANALOG_TV	2	Tuner supports analog TV
V4L2_TUNER_SDR	4	Tuner controls the A/D and/or D/A block of a Software Digital Radio (SDR)
V4L2_TUNER_RF	5	Tuner controls the RF part of a Software Digital Radio (SDR)

Tuner and Modulator Capability Flags

V4L2_TUNER_CAP_LOW	0x0001	When set, tuning frequencies are expressed in units of 62.5 Hz instead of 62.5 kHz.
V4L2_TUNER_CAP_NORM	0x0002	This is a multi-standard tuner; the video standard can or must be switched. (B/G PAL tuners for example are typically not considered multi-standard because the video standard is automatically determined from the frequency band.) The set of supported video standards is available from the struct v4l2_input pointing to this tuner, see the description of ioctl ioctl VIDIOC_ENUMINPUT for details. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_HWSEEK_BOUNDED	0x0004	If set, then this tuner supports the hardware seek functionality where the seek stops when it reaches the end of the frequency range.
V4L2_TUNER_CAP_HWSEEK_WRAP	0x0008	If set, then this tuner supports the hardware seek functionality where the seek wraps around when it reaches the end of the frequency range.
V4L2_TUNER_CAP_STEREO	0x0010	Stereo audio reception is supported.
V4L2_TUNER_CAP_LANG1	0x0040	Reception of the primary language of a bilingual audio program is supported. Bilingual audio is a feature of two-channel systems, transmitting the primary language monaural on the main audio carrier and a secondary language monaural on a second carrier. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_LANG2	0x0020	Reception of the secondary language of a bilingual audio program is supported. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_SAP	0x0020	Reception of a secondary audio program is supported. This is a feature of the BTSC system which accompanies the NTSC video standard. Two audio carriers are available for mono or stereo transmissions of a primary language, and an independent third carrier for a monaural secondary language. Only V4L2_TUNER_ANALOG_TV tuners can have this capability. Note The V4L2_TUNER_CAP_LANG2 and V4L2_TUNER_CAP_SAP flags are synonyms. V4L2_TUNER_CAP_SAP applies when the tuner supports the V4L2_STD_NTSC_M video standard.
V4L2_TUNER_CAP_RDS	0x0080	RDS capture is supported. This capability is only valid for radio tuners.
V4L2_TUNER_CAP_RDS_BLOCK_IO	0x0100	The RDS data is passed as unparsed RDS blocks.
V4L2_TUNER_CAP_RDS_CONTROLS	0x0200	The RDS data is parsed by the hardware and set via controls.
V4L2_TUNER_CAP_FREQ_BANDS	0x0400	The ioctl VIDIOC_ENUM_FREQ_BANDS ioctl can be used to enumerate the available frequency bands.
V4L2_TUNER_CAP_HWSEEK_PROG_LIM	0x0800	The range to search when using the hardware seek functionality is programmable, see ioctl VIDIOC_S_HW_FREQ_SEEK for details.
V4L2_TUNER_CAP_1HZ	0x1000	When set, tuning frequencies are expressed in units of 1 Hz instead of 62.5 kHz.

Tuner Audio Reception Flags

V4L2_TUNER_SUB_MONO	0x0001	The tuner receives a mono audio signal.
V4L2_TUNER_SUB_STEREO	0x0002	The tuner receives a stereo audio signal.
V4L2_TUNER_SUB_LANG1	0x0008	The tuner receives the primary language of a bilingual audio signal. Drivers must clear this flag when the current video standard is V4L2_STD_NTSC_M.
V4L2_TUNER_SUB_LANG2	0x0004	The tuner receives the secondary language of a bilingual audio signal (or a second audio program).
V4L2_TUNER_SUB_SAP	0x0004	The tuner receives a Second Audio Program. Note The V4L2_TUNER_SUB_LANG2 and V4L2_TUNER_SUB_SAP flags are synonyms. The V4L2_TUNER_SUB_SAP flag applies when the current video standard is V4L2_STD_NTSC_M.
V4L2_TUNER_SUB_RDS	0x0010	The tuner receives an RDS channel.

Tuner Audio Modes

V4L2_TUNER_MODE_MONO	0	Play mono audio. When the tuner receives a stereo signal this a down-mix of the left and right channel. When the tuner receives a bilingual or SAP signal this mode selects the primary language.
V4L2_TUNER_MODE_STEREO	1	Play stereo audio. When the tuner receives bilingual audio it may play different languages on the left and right channel or the primary language is played on both channels. Playing different languages in this mode is deprecated. New drivers should do this only in MODE_LANG1_LANG2. When the tuner receives no stereo signal or does not support stereo reception the driver shall fall back to MODE_MONO.
V4L2_TUNER_MODE_LANG1	3	Play the primary language, mono or stereo. Only V4L2_TUNER_ANALOG_TV tuners support this mode.
V4L2_TUNER_MODE_LANG2	2	Play the secondary language, mono. When the tuner receives no bilingual audio or SAP, or their reception is not supported the driver shall fall back to mono or stereo mode. Only V4L2_TUNER_ANALOG_TV tuners support this mode.
V4L2_TUNER_MODE_SAP	2	Play the Second Audio Program. When the tuner receives no bilingual audio or SAP, or their reception is not supported the driver shall fall back to mono or stereo mode. Only V4L2_TUNER_ANALOG_TV tuners support this mode. Note The V4L2_TUNER_MODE_LANG2 and V4L2_TUNER_MODE_SAP are synonyms.
V4L2_TUNER_MODE_LANG1_LANG2	4	Play the primary language on the left channel, the secondary language on the right channel. When the tuner receives no bilingual audio or SAP, it shall fall back to MODE_LANG1 or MODE_MONO. Only V4L2_TUNER_ANALOG_TV tuners support this mode.

Tuner Audio Matrix

	Selected V4L2_TUNER_MODE_
Received V4L2_TUNER_SUB_	MONO	STEREO	LANG1	LANG2 = SAP	LANG1_LANG2 [1]
MONO	Mono	Mono/Mono	Mono	Mono	Mono/Mono
MONO | SAP	Mono	Mono/Mono	Mono	SAP	Mono/SAP (preferred) or Mono/Mono
STEREO	L+R	L/R	Stereo L/R (preferred) or Mono L+R	Stereo L/R (preferred) or Mono L+R	L/R (preferred) or L+R/L+R
STEREO | SAP	L+R	L/R	Stereo L/R (preferred) or Mono L+R	SAP	L+R/SAP (preferred) or L/R or L+R/L+R
LANG1 | LANG2	Language 1	Lang1/Lang2 (deprecated [2]) or Lang1/Lang1	Language 1	Language 2	Lang1/Lang2 (preferred) or Lang1/Lang1

8.42.5. Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EINVAL

The struct v4l2_tuner index is out of bounds.

[1]	This mode has been added in Linux 2.6.17 and may not be supported by older drivers.

[2]	Playback of both languages in MODE_STEREO is deprecated. In the future drivers should produce only the primary language in this mode. Applications should request MODE_LANG1_LANG2 to record both languages or a stereo signal.